I feel like it's very seldom done on a straight wall without an Ollie in or help from transition. Slanted walls it's really just an exaggerated fs kickturn/drawn out fs carve on transition. I find them easier than bs on jersey barriers.
I've never done one on a straight wall but here's a video of a dude doing one. Play it slow and note how pointed his front foot is, just barely applying pressure and mostly guiding the nose up and then down.
It's probably just like doing one on a bank to wall with a more abrupt unweighting of everything besides the heel side of your back foot to get you up on that wall. Much easier said than done, for sure.
Here's another good video of a lot of different attempts. It's on a bank to wall, but the trick is probably mostly the same. Plus, Mike Anderson sw flips.